1. Field of the Invention
The present invention relates to a slide member made of an aluminum alloy, and more particularly, to a slide member made of an aluminum alloy and compositely reinforced at a sliding surface portion thereof by a reinforcing material.
2. Prior Art
One of such slide members made of an aluminum alloy and compositely reinforced at a sliding surface portion thereof by a reinforcing material is known from, for example, Japanese Patent Publication 3-71939 (1991), to comprise a reinforcing material made of a mixture of 8-20 vol. % alumina short fibers and 3-12 vol. % carbon fibers. In such a slide member, the combination of the alumina short fibers having a high hardness and the carbon fibers having a self-wettability furnishes the sliding surface portion of the slide member with an improved anti-wearing performance as compared with a slide member comprising a reinforcing material made of only the alumina short fibers.
However, the alumina short fibers and the carbon fibers are both relatively expensive, and therefore, the slide member reinforced by the combination of these fiber materials is expensive. Further, such a relatively high volumetric percentage of the hard alumina short fibers as 8-20 tends to increase the wearing of a mating member which slides against the slide member. Therefore, such a known slide member is not always most desirable for various purposes.
In view of the above-mentioned problems with respect to the prior art aluminum alloy slide member, it is an object of the present invention to provide a less expensive, high performance aluminum alloy slide member which is not only superior in the anti-wearing resistance of itself but also less abrasive against a mating member.
According to the present invention, the above-mentioned object is accomplished by a slide member made of an aluminum alloy and compositely reinforced at a sliding surface portion thereof by a reinforcing material, wherein said reinforcing material comprises a mixture of alumina short fibers consisting of not less than 80 wt. % alumina and the remainder silica and having 5-60 wt. % alpha alumina content, and non-spherical mullite particles consisting of 40-86 wt. % alumina and the remainder silica and having 3-60 microns mean diameter, the volumetric percentages of said alumina short fibers and said non-spherical mullite particles being 2-12% and 5-25%, respectively, on the basis of the volume of the reinforced portion.
According to the above-mentioned construction, the alumina short fibers having a high hardness provided by not less than 80 wt. % alumina with the alpha alumina content in a range of 5-60 wt. %, and the mullite particles of 3-60 microns mean diameter consisting of 40-86 wt. % alumina and the remainder silica, provide, in combination, and based upon such volumetric percentages as 2-12 and 5-25,respectively, an appropriately high hardness of the slide member itself, without increasing the wearing of a mating member, and further, since the non-spherical mullite particles are firmly held in the aluminum alloy matrix, a further improved anti-wearing performance of the slide member is available, together with an improvement of the wearing performance of a mating member, as compared with the prior art in which the reinforcing material is a combination of the alumina short fibers and the carbon fibers, as will be appreciated from the detailed descriptions made hereinbelow.
Further, according to the above-mentioned construction, since the content of the relatively expensive alumina short fibers is limited to be within a relatively low range such as 2-12 vol. %, while since the non-spherical mullite particles are less expensive than the carbon fibers, the slide member can be manufactured at a lower cost than the above-mentioned prior art slide member.
Further, when the total volumetric percentage of the alumina short fibers and the non-spherical mullite particles is made to be not less than 9%, not only the anti-wearing performance of the slide member and the wearing performance of a mating member are improved, but also the anti-scuffing performance of the slide member is improved, as described in detail hereinbelow.
As is well known in the art, the alumina-silica fibers are classified into alumina fibers, alumina-silica fibers and glass fibers according to the content of alumina, and although the borders between them are not very definite, it is generally admitted in this art that the alumina short fibers are alumina-silica fibers containing not less than 80 wt. % alumina. The condition xe2x80x9cnot less than 80 wt. % aluminaxe2x80x9d referred to in the present specification with respect to the alumina short fibers means that the alumina short fibers in the present invention contains 80 wt. % or more alumina as is generally admitted in this art.
The crystal of mullite is rhombic, and particularly a needle crystal. Therefore, when the mullite is mechanically pulverized, the needle crystal is torn off at a middle portion of its elongated shape, to produce irregular pieces having sharp edges quite different from the spherical or an ovally spherical shape of the particles produced by the atomization method or the like. The expression xe2x80x9cnon-spherical mullite particlesxe2x80x9d in the present specification refers to such angularly edged pieces each having at least one mechanically torn off surface, different from the spherical or ovally spherical particles.
Further, as is well known in the art, the theoretical composition of the mullite is 71.8 wt. % Al2O3xe2x80x9428.2 wt. % SiO2 (3Al2O3.2SiO2), and when the composition of the mullite particles deviates from such a theoretical composition, alumina crystals and/or silica crystals are generated in the mullite particles, in addition to the mullite crystals. The mullite particles used in the present invention contain 40-86 wt. % alumina, and therefore, the mullite crystals used in the present invention will include alumina and/or silica crystals to a certain corresponding extent.
The mullite particles used in the present invention are non-spherical, and so it is difficult to express the size thereof by the diameter. Therefore, the xe2x80x9cmean diameterxe2x80x9d with respect to the mullite particles described in the present specification is the conventional equivalent, corresponding to the diameter of a particle having the same volume as such an irregular mullite particle.